Products containing pentafluoroethane (i.e., pentafluoroethane products) are produced in various degrees of purity. HFC-125 is usually prepared by chlorofluorinating perchloroethylene to produce a mixture including 1,1,2-trichlorotrifluoroethane (CFC-113), 1,2-dichlorotetrafluoroethane (CFC-114) and 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123); removing 1,1,2-trichlorotrifluoroethane; and fluorinating the remaining mixture by various processes to produce a product containing pentafluoroethane (HFC-125) and chloropentafluoroethane (CFC-115) as well as smaller amounts of other fluorinated compounds (e.g., hexafluoroethane, FC-116). Various other methods for making pentafluoroethane also result in mixtures with significant amounts of chloropentafluoroethane. For example, HFC-125 can be produced by the hydrogenolysis of CFC-115 (see, e.g., Japanese Kokai No. 03/099026).
HFC-125 is a valuable non-chlorine containing fluorocarbon that is especially useful as a refrigerant, blowing agent, propellant, fire extinguishing agent or sterilant carrier gas. It has been found that for many of these applications, the presence of CFC-115 can significantly alter the physical properties of HFC-125. Furthermore, CFC-115 as a chlorine-containing halocarbon can reportedly have a deleterious effect on the stratospheric ozone layer. As a result, there have been continually increasing market and process demands for high purity CHF.sub.2 CF.sub.3. Consequently, identification of methods of separation represents a significant aspect of preparing HFC-125 for specific applications.
Purification of halogenated hydrocarbon products has been the subject of considerable research. Of particular interest are the challenges presented in separating a halogenated hydrocarbon from materials such as impurities in the starting materials used to produce the halogenated hydrocarbon, excess reactants, and reaction co-products and by-products which are difficult to remove by standard separation methods such as distillation. Mixtures of pentafluoroethane and chloropentafluoroethane can be nearly azeotropic. The boiling points of the halogenated hydrocarbons are very close (-48.5.degree. C. for pentafluoroethane and -38.7.degree. C. for chloropentafluoroethane). Furthermore, their relative volatility is below 1.1 at concentrations of pentafluoroethane greater than 87.5 mole percent and below 1.01 at concentrations of pentafluoroethane greater than 95 mole percent. The boiling points and relative volatilities indicate that it is extremely impractical to recover substantially pure pentafluoroethane from such mixtures by simple distillation.
Both carbon based and zeolite based sorbents have been proposed for various separations. The effectiveness of separation with either sorbent varies with the chemical components and the sorbents involved. The successful design of sorbent based systems is considered highly dependent upon experimental determination of whether the relative sorbencies of the particular compounds are suitable for such systems.